Organic electroluminescence display apparatuses (hereinafter, simply referred to as organic EL display apparatuses) are expected to replace liquid crystal display apparatuses, which are widely used today, and have been developed and made commercially available. Particularly, an active matrix organic EL display apparatus provided with a thin film transistor (TFT) as a switching device is considered to play a key role in a next-generation flat-panel display apparatus.
An organic electroluminescence device (hereinafter, simply referred to as organic EL device) provided in an organic EL display apparatus is constructed such that electrons and holes are injected into a luminescent layer from an electron injection electrode and a hole injection electrode, respectively. The electrons and holes are recombined at an interface between the luminescent layer and a hole-transporting layer or inside the luminescent layer in the neighborhood of the interface so that organic molecules are placed in an excited state. When the organic molecules are returned from the excited state to the ground state, fluorescent light is produced.
Generally, vacuum evaporation is used to manufacture an organic EL device. Unlike a liquid crystal display apparatus, an organic EL device of an organic EL display apparatus is itself a source of light of a specific color such as red, green and blue. Accordingly, a substrate should be patterned so as to form an organic EL device producing a desired color in a desired region. In a generally practiced method, a mask formed of a metal plate or the like provided with an opening is placed on a substrate. An evaporated material from a source of evaporation is selectively deposited on the substrate via the opening.
The mask for forming an organic EL device producing light of a desired color in a desired region on the substrate may be misaligned with the target region. As a result of misalignment of the mask, the luminescent layer may be formed in a region displaced from the target region. Consequently, the light-emitting region may be narrowed, the aperture for pixels may be narrowed and the yield of products may be lowered. Displacement of an organic EL device may cause a broken wire or a short circuit.